[Elecraft] KPA500 Hum

[Roy Morris]

Referring to kit assembly instructions, Rev B, June 22, 2011:
The following is on page 33.  When placing the transformer on the chassis 
you are told to press it toward the Z-Bracket so it does not hit the rubber 
bumpers installed earlier.  Then
above figure 49 on the same page it says the bumpers press
against the side of the transformer near the bottom.  Maybe some are
installing the transformer so it is resting against the Z-Bracket causing
vibrations (hum) and not firmly against the rubber bumpers as it should be.
Also some of the wires may be trapped (pressed) between the transformer and
the Z-Bracket causing the Z-Bracket to vibrate.  I snugged the transformer
against the rubber bumpers, and I can see light between the transformer and
the Z-Bracket.  I have not experienced any hum at all.  Roy  W4WFB